1. Field of the Invention
The present invention relates generally to flow control. In particular, the present invention is directed towards leak detection and backflow prevention (i.e., backflow reduction).
2. Description of Background Art
In many industries it is common practice to interconnect pressurized bulk liquid delivery systems for serving various processes. For example, in the semiconductor industry, most liquid chemistries are delivered under pressure to the wafer fabricating tools. Some of these chemistries are volatile, hazardous, toxic or otherwise chemically aggressive. It is often desirable to provide for the connection of facilities like deionized (DI) water to these bulk distribution systems providing a convenient method to flush-out and neutralize these chemical hazards for process reasons, including for example maintenance.
When two or more liquid delivery systems are interconnected (e.g., for process reasons) there is the potential for cross contamination. These intentional cross connections are often accomplished using valves such as check valves and three-way (or three-port) selector valves. If a small, internal leak (sometimes called a by-pass leak) occurs, the two or more liquids can migrate back and forth across the leaking valve seats contaminating or diluting the process chemistries.
In reality, all valves leak and check valves are particularly bad. Final test criteria for all valve manufacturers is essentially an acceptable leak rate. As valves age and normal wear takes place, leak rates increase. The problem leakage is reverse flow (or backflow). Often these reverse flows occur at very low flow rates [<5 ml/min] and are very difficult to detect. Yet these small leaks allow contamination or dilution of the cross connected liquids.
Backflow can cause expensive damage. High tech processes utilize high purity chemistries to ensure maximum yields and predictable performance. High purity chemistries are expensive. High tech manufacturing tools and fabrication facilities are also expensive. Cross contamination caused by backflow may lead to loss of productivity, reduced yields and semiconductor fabrication plant (FAB) shut downs. Unplanned shut downs to repair/replace leaking components and cleanup contaminated plumbing systems reduce financial performance and introduce unexpected delays into tight delivery schedules. It may take a long time before a small leak is discovered, resulting in the loss of much product and productivity. In bioprocesses, a single malevolent bacteria can ruin a whole batch, perhaps thousands of liters. In medical applications, contaminations can lead to illness, injury or worse.
In addition to contributing to backflow, by-pass leakages also waste valuable chemistries, damage expensive equipment, thereby causing excessive waste. Traditionally, by-pass leakages are detected through visual inspection, which is very insufficient because it is often difficult and time consuming. In addition, there are portions of systems that are difficult or impossible to view, and very small or intermittent leaks are easily overlooked.
Thus, there is a need for an ultra-sensitive leak detection device and a backflow prevention device for critical (or ultra high purity) materials applications.